This question can predict whether you will be alive and happy at age 80

Is there someone in your life whom you would feel comfortable phoning at four in the morning to tell your troubles to? If your answer is yes, you will likely live longer than someone whose answer is no. For George Vaillant, the Harvard psychiatrist who discovered this fact, the master strength is the capacity to be loved. Conversely, as the social neuroscientist John Cacioppo has argued, loneliness is such a disabling condition that it compels the belief that the pursuit of relationships is a rock-bottom fundamental to human well-being.

And:

Vaillant’s insight came from his seminal work on the Grant Study, an almost seventy-year (and ongoing) longitudinal investigation of the developmental trajectories of Harvard College graduates. (This study is also referred to as the Harvard Study.) In a study led by Derek Isaacowitz, we found that the capacity to love and be loved was the single strength most clearly associated with subjective well-being at age eighty.